Treating zinc with organic acids



Patented July 29, 1941 U TED PATENT TREATING z n'vo WITH ORGANIC ACIDS John S. Thompson'and Edward S. Hanson;

' 3 Detroit, Mich. i

No Drawing. Application June- 15, i936, Serial N o ."85,335-.; 'lteneyved January'20, 1939-... f t

1 This invention relates to-the field-of chemically:

treating metal surfaces.- Moraparticuiarlm it has to dowith the coatingcf zinc-surfaces for the purposeof increasing the-corrosion resistance thereofand to assist said surface in retaining siccative coatings such as paints, lacquers, enamelsand the like.

Inthepast, several organic acids have been i used for the purposes aforesaid, including acids taken from the groups of dicarboxylic and hydroxydicarboxylic acids of the aliphatic series, andalso carboxylic acids withone carboxyl group and sulfonicacids'of the aromatic series.

Ithas been discovered that beneficial treatmentsof zinc surfaces are obtained by subjecting the metallic surfaces to the action of solutions containing. one or more 'of the following groups of acids and mixtures:

1. Aromatic series of acids having two carboxyl groups. l

2. Mono-carboxylic acids of the aliphatic series. f

3. Tri-carboxylic acids of the aliphatic series.

4. Hydroxy mono-carboxylic acids of the aliv phatic series,

The following way. of limitation.

Example 1.-A 2 solution of phthalic acidff containing 1% ferric sulfate will produce a black coating on zinc surfaces in four minutes at boiling temperature. The addition of sodi nitrate produces a gray coating on zinc surfa in three minutes at boiling temperature; 1.

Example 2.--A 2 solution of formic acid; containing 1% ferric. sulfate coats zinc surfaces 5 in five minutes at boiling temperature. The same ,W sodiunijnitrateisadded to this solution a coating composedprincipally of oxides is formed in fiye minutesIatroonrtemperaturel'fAt 1 boiling temperature this solution'producesalcoat-l,

ing composed minutes. 7

Example f6.-.-A

principally of. citrate naemic-.1; of glycol-11c acid containing,,1% ferricisulfat'eproduces asm udgy' 1 j a black coating on ainclinfour-:minutes at r examples are given with the intention of illustrating the invention and not byg solution plus /2% sodium nitrate produces aha-rd reddish coating on. zinc at room temperature in five minutes.

Example 3.-A 2 solution of acetic acid,

containing 1% ferricsulfate and sodium nitrate producesa hard yellow coating on zinc in five minutes at room temperature. The, same 7 solution when used at boiling temperature pro-' duces a heavy gray coating. h

Example 4.A 2'/z% solution of propionic acidv containing 1% ferric sulfate will coat zinc in three minutesat boiling temperature. The same solution containing /2% sodium nitrate produces a black coating on zinc in three minutes at room I temperature. v

Example fir-A 2 solution of citric acid containing ferric sulfate produces a black coating on zinc in two minutes at boiling temperature.

- tempera. ure. The-same solution when boiling" t, inperature produces a. hard blac ing in three minutes. When A; sodium nitrate. is added to the soluticna, good gray coating fee} sults in three minutes at boiling temperature.

Example 7. gz s'oiuti'on of jrnandelic acid I 1 containing 1%Trric sulfate'rproduces a gray coating in ten minutes a't -bo'iling' temperature. The same, solution withf theaddition ,of /2% sodium nitrate produces a:- gray coating in 15 minutes at room temperature." The latter solua tionjzproduces hard gray coating iu four minutes when usedj at boiling temperature.

will be nde'rsto'tlthat coatingsf-on' surbtained h one of three combinaithrone Gfitlie acidsin the above and a jm'etal afcc'elerator; third, one of the acids r a nd an oxidizing agent.

containedu inthe groups listed above, a metal accelerate 5 It. a e reac ion that takes place between strong oxidiz ng' agents and some organic acids the oxidizing agents suitable for use in these combinations sodium nitrite and sodium bromate.

It has also been discovered that a number of metals'act as accelerators in these solutions; The

metals may be added to the solutions in the form of soluble salts 'or compoundsand it seems to be immaterial what salts are used. Metals which examples forferric sulfate inthe same propor- -i i ps jar d an oxidizing agent second, onev ids coritained in the groups listed above 7 ve readily understood that because of I are necessarily limited to those which do not readily oxidize the acid being used. Among the 'suitablefoxidizing, agents are nitrates, nitrites and 1 bromates such as sodium nitrate, zinc nitrate,

tions except in the case of antimony and copper Where all that is needed is 0.05 to 0.1% potassium antimony tartrate or 0.525% copper sulfate, or less.

Both the oxidizing agent and the metal accelorator may be added in the same compound such as by making use of nickel nitrate, copper nitrate or cobalt nitrate.

The solutions used in this invention may be ap-- plied to the metal surface in any convenient waysuch as by the immersion method whereby the articles to be coated are submerged in thesolution until action is complete; spraying by means of a mechanical spraying machine wherein the solution is sprayed onto the surface to be coated, drained off, collected and resprayed; or bymaking use of an ordinary compressed air spray gun.-

which sprays a thin film of solution onto the sur-- face to be coated, both with and without a finely divided inert material to hold the solution in place until the reaction is complete.

Coatings on zinc obtained from the various combinations provided for herein are ofthree different types. coating such as is produced from a solution containing a ferric salt and an oxidizing agentwith' the acid, such as a solution of citric acid, ferric sulfate and sodium nitrate, used at room temperature. The second is a zinc oxide coating with the basic salt of the metal in the accelerator such as is produced in a solution containing acetic acid, ferric sulfate and sodium nitrate when used at room temperature where a basic ferric sulfate- The first is a magnetic oxide is formed. The third is the organic salt of zinc such as is produced in a solution of citric acid,

ferric sulfate and sodium nitrate when used at boiling temperature. i

A method of producing the first type of coating specified above is disclosed more broadly and claimed in the copending application of John S'.

Thompson, Serial No. 390,337, filed April 25, i941,v

nitrate and chromic nitrate or sulfate. The solu-- tions may be used from room temperature up to boiling but where chromic acid is used it is pref erable to use it at room temperature or slightly above as it tends to react with organic salt coatings at the higher temperatures.

From 2 to 6 grams of the acid or salt per gallon is the preferred strength from the standpoint of economy, although stronger solutions may be used to advantage. A treatment of oneminutein the solution is sufficient. If I The above detailed description is given with the intention of illustrating-Rho; invention, the scope of which'is to be determined from the appended claims.

What we cl aim is 1 l. A metliodof chemically coating zinc surfaces which consists in subjecting said surfaces to the action of a solution composed principally of an acid of the group consisting of the aromatic series of .acids having two carboxyl groups, the

mono-carboxylic acids of the aliphatic series, the

tri-carboxylic-acids ofi'ther aliphatic series, and. the hydroxy mono-carboxylicacidsoi'Tthecaliiphatic series until a visible protectlvercoating is obtained on thezzinc surfaces.

2. A method? of chemically'coating;:zinc sur--- f aces whichtcomprisessubjecting, said. surfaces to r the actionzof a. solution: composediprincipally of i' an I acid. of the; groupi consistingcof the; aromatic series. oi? BClClSz hsvingz-twoz" carboxyl groups, the I mono-carboxylicmcidsrofithaaliphatic series,- the tri-carboxylic: acids.- oil thealiphaticseries, and L the hydroxy' monorcarboxylicr acids of i' the all--- phaticseries; .andfcontaining; anmetalf accelerator;

in the forn'r ofl a soluble; compound? of a metal beingtone of ithe=group of iron, antimony," arsenic,

zinc; cobalt,. copper; nickel? cadmiumfluntil' a1visible protectiva-coatingris-.obtained"on thc:zinc surfaces:

3.- A metliodf of?" coating: sur

faces which comprisestsuhjectingisaid isurfaces to; the .action' or? arsolutiomcomposedlprlncipfll'y; of. an acid of a the groupr cousi'stingi. of? the aromatic series; of acids having; two: csrhoxyii groups; the

mOIIO-OBIDOXYHC'. acids :ofithevaliishntic: series: the: tri-carboxylio" was offth'e aliphatict the hydroxy: mono carboxylic acids? or. the: allphatic' series; and cont'aixflhgzamoxidilihgj Merit which doesnotireadllw oxidize.the.lmidiusedzuntil a visible'protective coatingisohtained'onathez zinc. surf aces;

4. A method of chemically coatings zinc: sur-- faces which comprises subiectingzsaidpurfacesto:

the 7 actionof) a' solution containing an acid; of

face having a coating imparted thereto by! the action of a solution composed principally of an acid of the group consisting of the' aromatic series of acids having two carboxyl" groups, the mono.- carboxylic acids-of the aliphatic series, the trioarboxylic. acids of the aliphatic. series, and the hydroxy mono-carboxylic: acids: of the aliphatic series.

6. An article having a'suriace of 'zinc', such surface havinga coating imparted thereto bytheaction of a solution composed principallyof an'acid of the group consisting-0f? the aromatic series of acids having two carboxyl groups, the monocarboxylic' acids of the. aliphatic series, the tricarboxylic acids. of the aliphatic series, and the. hydroxy' mono carboxylic acids of the. aliphatic: series, and a metal accelerator in. the form oila soluble compound of a metalrbeingone'of. the

group of" iromantimony, arsenic, zinc; cobalt, copper, nickel and cadmium:

7. An article having a surface of zinc, such.

surface-having a1coatingalmpartedtheretoby the action of a.l solutiom composed principally ofv an acid: of the group; consisting of. the aromatic series of acids having-itwocarboxylgroups, the mono-'carboxylicacids ofthealiph'atic series, the

tri-carboxylic" acids. of the. aliphatic. series, and.

the hydroxy mono-carboxylic acids oi thealiphatic series, andz'containingvan oxidizingzagent which does. not readily oxidize the acid'zused.

8. An article having a surface of zinc, such surface having a coating imparted thereto by the action of a solution composed principally of an acid of the group consisting of the aromatic series of acids having two carboxyl groups, the mono-carboxylic acids of the aliphatic series, the tri-carboxylic acids of the aliphatic series, and the hydroxy mono-carboxylic acids of the aliphatic series, and containing an oxidizing agent chosen from the group consisting of nitrates, nitrites and bromates, and a metal accelerator chosen from the group of iron, antimony, arsenic, zinc, cobalt, copper, nickel and cadmium.

9. A method of chemically coating zinc surfaces which comprises subjecting said surfaces to the action of a solution containing as a main coating chemical one of the group consisting of phthalic, formic, acetic, propionic, citric, glycollic and mandelic acids and containing a metal accelerator in the form of a soluble compound of a metal being one of the group of iron, antimony, arsenic, zinc, cobalt, copper, nickel and cadmium until a visible protective coating is obtained on the zinc surface.

10. A method of chemically coating zinc surfaces which comprises subjecting said surfaces to the action of a solution containing an acid as a main coating chemical of the group consisting of ,phthalic, formic, acetic, propionic, citric, glycollic and mandelic and containing an oxidizing agent which does not readily oxidize the acid used until a visible protective coating is obtained on the zinc surface. 1

11. A method of chemically coating zinc surfaces which comprises subjecting said surfaces to the action of a solution'containing an acid of the group consisting of phthalic, formic, acetic, propionic, citric, glycollic and mandelic, an oxidizing agent chosen from the group consisting of nitrates, nitrites and bromates, and a metal accelerator chosen from the group of iron, antimony, arsenic, zinc, cobalt, copper, nickel and cadmium until a visible protective coating is obtained on the zinc surface.

12. An article having a surface of zinc, such surface having a coating'imparted thereto by the action of a solution composed principally of an acid of the group consisting of the aromatic series of acids having two corboxyl groups, the mono-carboxylic acids of the aliphatic series, the tri-carboxylic acids of the aliphatic series, and the hydroxy mono-carboxylic acids of the ali phatic series, and containing an oxidizing agent which does not readily oxidize the acid used, and a metal accelerator chosen from the group of iron, antimony, arsenic, zinc, cobalt, copper, nickel and cadmium.

13. An article in accordance with claim 12 and wherein the coating contains as an essential ingredient, magnetic oxide formed at substantially room temperature in a solution containing a ferric salt as a metal accelerator.

14. An article in accordance with claim 12 and wherein the coating contains as an essential ingredient, a basic salt of the metal accelerator.

15: An article in accordance with claim 12 and wherein the coating consists ganic salt of zinc.

JOHN S. THOMPSON. EDWARD S. HANSON.

principally of an or- 

